1. Field of the Invention
The process and apparatus described herein relates to devices for the detection of contaminant particles contained in vials or flasks, and particularly for the detection of particulate matter in liquids intended for pharmaceutical use.
2. Background Information
In the pharmaceutical industry, vials containing parenteral substances and flasks containing liquids for intravenous infusion must be inspected to determine the presence of undesirable solid particles in the liquid. This determination is a very important problem, and until now a delicate and time consuming process.
With current techniques, inspection of individual containers prior to their packaging is performed either manually or automatically by means of suitable machines. In machines for manual inspection, the vials or flasks are made to rotate very rapidly after being inserted between a mandrel and chuck arrangement that is free to rotate. After a certain period of time, the containers are abruptly stopped, and a beam of light illuminates the container, either from below or laterally, so that an operator can manually observe any particles set in motion by the residual motion of the fluid. Such a manual process is particularly inconvenient, imprecise and costly.
Prior automatic machines used to detect spurious solid particles involved transmitting an image of the container on a television picture tube or onto an array of photodiodes. In the former, after the container's rotation is stopped in a fashion similar to the manual process, the picture tube captures various images of the container in rapid succession. Every image is stored in memory in an electronic computer, and then compared among themselves point by point. If differences among the various images are detected, this signifies that the liquid contains particles which are successively occupying different positions, and the container is consequently discarded.
In machines used currently, illumination of the vial can occur through the bottom of the container, in which case the particles become the source of a diffused light which generates the visible image. In other cases, light is emitted coincident with the direction of observation, in which case the presence of the particles produces a darkening of the image at those points where they are located. In any case, the use of visible light, i.e. wide-band spectrum radiation, also requires consideration and protection from interfering ambient light sources such as room light. In the past, covers, tinted shields, or other protective measures were necessary to ensure efficiency.
In machines where the image is displayed on an array of photodiodes the number of points in the image that need to be placed in memory is reduced. In this case, however, what is inspected is not the entire container but only a portion of it, generally concentrated around the axis of rotation and of a length equal to the height of the meniscus. This involves a reduction in the system's probability of detection, since on the one hand the positions of the particles within the liquid are random, and on the other, the detector element is concentrated only on a partial area of the liquid itself. This problem has been overcome by performing two inspections at two independent and successive inspection stations. The containers discarded are those which show the presence of particles at least at one of the two observation stations.
The methods described, even allowing a sufficient level of reliability in inspection, require complex and expensive electronic components such as vidicon-type or solid-state type television cameras, photodiode arrays, fast analog-digital converters, and high-speed computers to record and compare the images.
It should be remembered that to be profitable, a container inspection machine must be capable of inspecting several thousands of units per hour.